1. Field of Invention
The invention relates to an optical disk differentiating method and an electronic device thereof, and in particular to an optical disk differentiating method with dynamic calculation and an electronic device thereof.
2. Related Art
Digital versatile disks (DVDs) are a new generation of optical information storage medium having a higher data density and a larger capacity than those of the compact disks (CDs), and DVD drives have become the mainstream peripherals in the market. A lot of data are stored in the CDs in the past CD generation, so that the optical disk drive must have the ability of reading the CDs and DVDs in order to satisfy the user's demands. Thus, the problem of compatibility has to be considered when the optical disk drive is designed. That is, the optical disk drive must have the ability of reading various CDs (CD-ROM, CD-R, CD-RW) and DVDs (DVD-ROM, DVD-R, DVD+R, DVD-RW, DVD+RW).
FIGS. 1A and 1B are cross-sectional views showing a conventional CD and a conventional DVD.
The typical DVD 1 includes a dummy substrate 11 with the thickness of 0.6 mm, and a data substrate 12 with the thickness of 0.6 mm. The data substrate 12 is bonded to the dummy substrate 11 to form the DVD 1 having the thickness of 1.2 mm. The data substrate 12 includes a pre-grooved substrate 121, a recording layer 122 formed on a surface of the pre-grooved substrate 121, and a reflective layer 123 formed on the recording layer 122. Then, the dummy substrate 11 and the data substrate 12 are bonded together through a bonding layer 13 to form the DVD 1.
The typical CD 2 has the thickness of 1.2 mm and includes a pre-grooved substrate 211, a recording layer 212 formed on a surface of the pre-grooved substrate 211, a reflective layer 213 formed on the recording layer 212, and a printed layer 214 formed on the reflective layer 213.
The conventional method of differentiating the type of the optical disk is made according to the difference between the thickness of the DVD 1 and the thickness of the CD 2. Typically, the optical pickup head is moved to output a laser beam travelling toward a to-be-tested optical disk, and the laser beam touches the to-be-tested optical disk and is then reflected by the optical disk to generate a reflex signal. The optical disk may be the CD or the DVD, and the laser beam first touches the substrate 121 or 211 of the to-be-tested optical disk and then touches the recording layer 122 or 212 of the to-be-tested optical disk. Because the energies reflected by the substrate 121 or 211 and the recording layer 122 or 212 are different, the optical disk drive calculates the difference between the time when the substrate 121 or 211 generates the reflex signal and the time when the recording layer 122 or 212 generates the reflex signal. Then, the difference is compared with a constant threshold value in order to judge whether the optical disk is the CD or the DVD.
However, the moving speeds of various optical pickup heads manufactured by various factories are different. More particularly, 50% of error is allowed in the specification of the shipped out product. Thus, the possibility of misjudging the type of the optical disk in the optical disk drive is greatly increased when the optical disk drive judges the type of the optical disk according to the time difference of the reflex signal and the constant threshold value.
In the condition that the moving speeds of the optical pickup heads cannot be unified, how to precisely judge the type of the optical disk is an important subject.